Switchgear assemblies form components for electrical power transmission and distribution. Their versatile capabilities and complex functions can, on the one hand, contribute to general safety, and on the other hand can ensure the availability of electrical power.
The basic design of known medium-voltage switchgear assembly, for example, includes a primary part and a secondary part. The electrical power is distributed via the primary part while the secondary part controls and monitors the primary switching devices and circuits.
Depending on the customer's philosophy and requirement profile, widely different equipment can be used for the secondary technology.
In principle, a distinction is drawn in secondary technology between switchgear assembly control and switchgear assembly control assisted by a microprocessor.
In the case of microprocessor-assisted assembly control, programmable logic multifunctional relays carry out numerous functions such as protection, control, measurement, monitoring and visualization of the switchgear assembly.
By way of example, a multifunctional relay is known, such as the REF542plus from ABB, which offers the capability for freely programmable control of the required functions, and their assignment to virtually any desired binary inputs and outputs. This allows the system designer a high degree of standardization for his secondary-technical components and their wiring.
The high degree of standardization assists the use of plug connectors and prefabricated cable harnesses. This makes a major contribution to high secondary technology availability. An exemplary advantage of this technique is the maintenance-friendliness.
Secondary technology can be implemented using discrete equipment such as pushbuttons, signaling lights, display instruments for current, voltage, etc., measured-value converters, protective relays, auxiliary relays and mechanical auxiliary switches.
The functions can be produced by wiring the individual equipment/components to one another. Owing to the multiplicity of possible functions and the equipment that is used in this case, a standardized wiring configuration is not practical.
The various installation locations of the numerous equipment items in the control cabinet and in the control cabinet door result in the following exemplary disadvantages:                Increased use of terminal blocks because of the multiplicity of interfaces.        The use of prefabricated cable harnesses is not practical, because of the large number of installation locations and equipment items.        Lack of electrical plug connections on the components.        Large amount of interconnection effort to produce all the functions.        Wiring technology that is not maintenance-friendly.        